1. Field of the Invention
The invention relates in general to a power supply controller for a computer system and, in particular, to a secure power controller for a computer system.
2. Description of Related Art
In typical microprocessor-based personal computer or workstation systems, simple mechanical on/off contact switches are used to supply or cut-off electrical power to the power supply unit of the computer systems. When the mechanical contact switch is turned on, the closed-circuit switch supplies electrical power, such as 110V AC, to the power supply circuitry which converts the AC power into the appropriate DC power. With a steady supply of all the necessary DC power, the computer system initiates its start-up sequence, and the system boots up. These mechanical contact switches are turned on and off by a human. Many computer systems have no other means to turn power-on or -off.
Many of these systems have no security. Once the main power switch is switched and maintained on, the system starts a sequence of operations. If no effective password control scheme is incorporated at either the system firmware or the operating system level, once powered up, the entire system, together with all its data, is exposed to anyone having access to the system.
Models of the Macintosh series of personal computer systems manufactured by Apple Computer Inc. of Cupertino, Calif. employ a designated key on the keyboard to control powering up and down. Though convenient, this keyboard also lacks effective security. Once a system has its power cord connected in the utility socket, anyone who can get access to the computer by depressing the power up key on the keyboard. Firmware and/or operating system level program routines similar to those mentioned above would have to be used to provide access restriction for these computer systems.
On the other hand, the ATX standard computer motherboard includes a power supply subsystem that does not rely on the simple mechanical contact switch. Instead, the ATX implements a form of soft power control under supervision of a circuitry integrated in the computer system itself. It provides power for basic power management circuitry in the computer system when the main power supply is cut off. The power management circuitry may be programmed to implement various functions of the computer system. For instance, the system can be programmed to start itself automatically at midnight when unattended by an operator so as to send international facsimile transmissions during a discount rate time period of the telephone company. The computer system also may be awakened in the evening by incoming requests for remote modem connection in order to receive file transmissions.
However, such concepts of soft power management as implemented by recent standards such as ATX, still lack the security measures. When a computer system adopting the ATX standard is started by a user (either authorized or not) by switching-on the main power switch, the power supply is then turned on, and the system initiates its start up sequence of operations. At this moment, anyone having direct access to the system has access to the data contained in the computer. Such systems are as unprotected as were the earlier generation of computers having a mechanical main power switch.
Some conventional computer systems are equipped with a firmware or operating system-level security system that requires a password for entry after the computer is powered up. Typically, the user can try a limited number of times to enter the password. If after the specified times of trial, the user still does not enter the correct password, the system simply locks and ignores all keyboard or other inputs. In this case, the user will have to turn off the power to the computer system and then turn it back on again and try entering more passwords. This process of power-on and -off must be performed repeatedly before the correct password is entered if a user wishes to keep trying to break into the system. During this process of repeated switching-on and -off of the main power supply, the computer system is exposed to increased possibilities of premature failure.
FIG. 1 shows a conventional mouse controller interface 12 that acts as an interface between the computer system motherboard 10 and its external mouse unit 20. Motherboard 10 is connected to power supply unit 30. The mouse unit 20 has a microcontroller and mouse scanning circuitry (not shown in the drawing) installed internally. Typically, serial communication is used to establish connection between the motherboard 10 of the system unit and the mouse unit 20 signals MDATA and MCLK. Signals MDATA and MCLK are used to establish a connection between the mouse unit 20 and the mouse controller 12. Power V.sub.DD and ground GND paths are also connected between the mouse controller 12 and mouse 20.
Existing microprocessor-based computer systems operate on power supply subsystems that do not allow, or at least do not recommend, repeated switching-on and -off during a short period of time. Some power supplies are equipped with protection circuitry that prevents them from powering-on within a specified time period of, for example, a few seconds after being turned off. Though circuit boards in a computer system can thus be protected from potential damage in successive power-on and -off sessions, other components such as disk drives are not as protected. This is because spindle motors for modem hard disk drives are not designed for repeated power changes. They are designed to be turned on with power maintained for a long period of time.
It would therefore be desirable to have a security control apparatus on the computer power supply subsystem that determines whether a user is allowed access to a computer system before powering-up the computer system. This would provide security and prevent physical damage to components in the computer system due to repeated power changes.